1. Field of the Invention
The present invention relates to a thin film magnetic head and a method for manufacturing thereof.
2. Description of the Prior Art
The majority of thin film magnetic heads employed in a magnetic disk apparatus constituting storage systems for computers in recent years adopt a combined structure in which a thin film write element and a magnetoresistive (hereafter referred to as MR) read element are provided.
An MR read element is capable of achieving a high degree of resolution regardless of its speed relative to the magnetic disk. The MR read element includes a first shield film, a second shield film and an MR element. The first shield film and the second shield film are separated from each other by an appropriate non-magnetic insulator, with the MR element provided between the first shield film and the second shield film.
An inductive electromagnetic transducer is employed to function as a write element and is laminated onto the MR read element. The inductive thin film magnetic transducer constituting the write element is provided with a first magnetic film which also functions as the second shield film for the MR read element, a second yoke, a gap film and a coil film supported by an insulating film constituted of an organic resin and the like.
The front ends of the first magnetic film and the second yoke respectively constitute a first pole tip and a second pole tip that face opposite each other over the gap film having a very small thickness, and write is performed at the first pole tip and the second pole tip.
The yokes of the first magnetic film and the second magnetic film are linked to each other at the back gap portion located on the opposite side from the first pole tip and the second pole tip to complete a magnetic circuit. The coil film is formed to wind around the linking area of the yoke in a coil.
In order to achieve a high recording density by using this type of thin film magnetic head, the quantity of data stored per unit area of the magnetic disk (areal density) must be improved. The areal density is affected by the capability of the write element. The areal density can be improved by reducing the size of the gap between the poles at the write element. However, since reducing the size of the gap leads to a reduction in the magnetic flux intensity between the poles, there is naturally a limit to the extent to which the gap size can be reduced.
Another means for improving the areal density in recording is achieved by increasing the number of data tracks that can be recorded on the magnetic disk. Normally, the number of tracks that can be recorded on a magnetic disk is expressed as TPI (tracks per inch). The TPI capability of the write element can be improved by reducing the head dimensions, which determine the data track width. These head dimensions are normally referred to as the head track width.
One of the problems with the thin film magnetic head in the prior art described above is that, since the first magnetic film of the write element also functions as the second shield film for the MR read element, the track width at the first pole tip cannot be reduced, which results in a rather large side fringing magnetic field generated during recording. This magnetic field is caused by a leak of the magnetic flux from the second pole tip where the track width is reduced to the first magnetic film where the track width is not reduced. Such a side fringing magnetic field restricts the degree to which the track width can be reduced and consequently, limits the degree of improvement that can be achieved with respect to track density. In addition, it degrades the off-track performance when previously written track data are read by the MR element.
Japanese Unexamined Patent Publication No. 262519/1995 and Japanese Unexamined Patent Publication No. 225917/1995 disclose a means for matching the track width at the first pole tip to the track width at the second pole tip through ion beam milling. However, employing such means may cause problems such as particles resulting from the ion milling process becoming re-laminated onto the side wall of the second pole tip or the first pole tip. A portion that is formed as a result of such re-adhesion presents a hindrance to setting the track width at the write pole to a very small value with a high degree of precision. In addition, since the magnetic characteristics of the portion formed as a result of the re-adhesion will be degraded under normal circumstances, re-adhesion is not desirable in the sense that it works against achieving an improvement in the magnetic characteristics.
In addition, in this type of combined thin film magnetic head, the insulating film supporting the coil film is raised to a considerable degree. Because of this, when a photoresist is laminated during the photolithography process for forming the second yoke, the photoresist adheres over the great thickness at the portion with level differences. Consequently, the pattern at the second pole tip formed under the portion with level differences must be formed through the photoresist having a large film thickness, resulting in a markedly high aspect ratio (ratio of height to width of the resist). Thus, this is a negative factor in minimizing the track width.
In the prior art technology disclosed in Japanese Unexamined Patent Publication No. 28626/1994, after forming a first magnetic yoked layer (first yoke), a photoresist layer is laminated and an opening portion for forming, through patterning, a magnetic pole tip assembly constituted of a first pole tip, a gap film and a second pole tip is formed at the photoresist layer. Then, after the magnetic pole tip assembly is formed at the opening portion, the photoresist layer at the front of the magnetic pole tip assembly is removed. Next, the photoresist layer is hard-baked to form a flattened insulating layer. After this, a coil structure, an insulating film and the like are formed by adopting a method in the prior art and then a second magnetic yoked layer (second yoke) is formed. One of the problems with this prior art technology is that the photoresist layer, which cannot be readily flattened due to its fluidity and the like, must be used as a flattened film, and another problem is that the width of the second magnetic yoked layer (second yoke) in the direction of the tracks is smaller than that of the magnetic pole tip assembly.
Alternatively, in the prior art technology disclosed in the publication above, after a first magnetic yoked layer (first yoke) is formed, a photoresist layer is laminated, an opening portion for forming, through patterning, a magnetic pole tip assembly constituted of a first pole tip, a gap film and a second pole tip is formed at the photoresist layer, a coil structure, an insulating film and the like are formed after forming the magnetic pole tip assembly within the opening portion and then a second magnetic yoked layer (second yoke) is formed. A problem in this case is that since the second yoke must be laminated onto the magnetic pole tip assembly within the opening portion, the adhesion of the second yoke to the magnetic pole tip assembly tends to be problematic when the track width is reduced.